Most people tend to 4bet AKs and call AKo against 3bets in earlier position RFI's.
So if you open AKo UTG or MP and then get 3bet you can call AKo.

If you go for a population exploit and notice people tend to not 3bet bluff enough then you can either call AKo more and hope to connect. As most people tend to bet on Axx boards anyway. Or have weaker AX in their range.
Or you can 4bet AK and then I would call the 5bet.

It might be that you will be flipping or behind when they do call your 5bet. But you should still generate some money from their folding range. If you notice they never fold, then their 3bet range is much too strong and I would just call AK.

I do think an overbluff is possible yeah. His overbet on turn on such a board is very draw heavy.
Only the club draw gets there on the river, which we block with the 9c.
So in theory our 99 is a bluffcatcher in a spot where he shouldn't have thin bets (due to turn sizing). And we block some value so seems fine.

Yeah I was also thinking about if this could be a potential river sizing tell -- since OOP shouldn't have thin value bet in theory, the medium size bet feels like two pair wants to get value and bet fold to flush or exact hands he has -- too strong so he sized down to get called. Instead his JT/T9/naked diamond will probably overbet again OTR?

So on the river, the medium sizing is probably more value heavy vs the overbet line? What do you think about this -- am I reading too much into the sizing?

Makes sense that the nuts and nut blockers want some overbet sizing.
But there are enough other hands such as 2p that still want value. So I think his sizing makes a lot of sense, both with value and bluffs.
I wouldn't read too much into the river sizing here. I mainly went with the turn range he should have. And then that he has to be quite carefull not to overbluff on river with that range.

I actually have a hard time hearing my own statement there at the end. Not sure I'm saying I will check call anyway. When I slow it down it sounds like "Am I going to check call anyway?". So I'm posing the question to myself.

Looking at it now. I would say I would check fold as I don't think people will bluff enough. Blockbet is still nice to get value from worse hands. But if they don't bluff enough then surely we get to showdown quite easily. And have an easy fold against the bet. I think either option is fine. Prefer the blockbet a bit as it seems closer to what I assume GTO would do. Mix in some strong hands to call the raises in theory.

Yeah that would make sense if it's a question instead of a statement :D
Thank you!

I also just checked in a solver. It blockbets very often on the river, including TT.